1. Field of the Invention
The present invention relates to media copy protection, and more particularly, to a digital media copy protection method that provides a secure copy control of the digital media using hybrid cryptographic and watermarking techniques and an authenticated handshake protocol.
2. Discussion of the Related Art
Communication systems such as computer networks, telecommunication systems, and other systems are increasingly using cryptography for the security of information. There are two main classes of cryptographic systems: symmetric key and public key cryptographic systems. In a symmetric key cryptographic system, a symmetric (secrete) key is used for both of data encryption and decryption processes. There are several efficient implementations of the symmetric key cryptographic system, but the actual key managements of such implementations are often troublesome.
On the other hand, in a public key cryptographic system, the data encryption and decryption processes are independent from each other. That is, the data encryption process requires a public key, often designated as e, while the data decryption process requires a different (but mathematically related) private key d. Therefore, an entity being possessed of the public key may encrypt a plaintext, which is the original form of a message, but the entity may not be able decrypt a ciphertext, which is the encrypted form of the message.
If an entity selects a public key and publishes the public key, anyone is able to use the key to encrypt one or more messages for the entity. Then the entity keeps his private key secret so that he or she is the only one who can decrypt the ciphertexts of the messages. The implementations of the public key cryptographic system are currently less efficient than those of the symmetric key cryptographic systems, but they are much safer.
In a hybrid cryptographic system, a plaintext is encrypted with a symmetric key corresponding to a symmetric algorithm. The symmetric key is then encrypted with a public key corresponding to a public algorithm. When a receiver receives the public key-encrypted symmetric key and the symmetric key-encrypted data, the receiver initially decrypts the symmetric key by using his own private key. Subsequently, the receiver decrypts the encrypted data by using the decrypted symmetric key. The processes of obtaining the original data in a hybrid cryptographic system are usually faster than those of the public key cryptographic system. In addition, a hybrid cryptographic system may allow using a different symmetric key each time, considerably enhancing the security of the symmetric algorithm. For that reason, the hybrid cryptographic systems are ideal for transferring the protected media data safely to a receiver.
Watermarking is a technology, in which copyright information (information indicating a copy guard) is expressed by a watermark superposed in media data. Such information is embedded into various media data including image data and sound data, and it should be invisible and inaudible to a human observer. The purpose of superposing a watermark in the media data is to provide a proof of a copyright so that an illegal use and copy of the media data can be prevented. Therefore, the copyright information should stay stable in a host signal even when the host signal is subjected to any data process.
The technique for superposing a watermark in the media data depends on the size of the watermark data and the invariance of the watermark data to any data process of a host signal. There is a watermark inherent trade-off between the human perceptibility, bandwidth, and robustness (i.e., the degree to which the data are immune to be attacked or transformations that occur to the host signal through a normal usage). The more data to be superposed, the less secure the encoding process is. The less data to be superposed, the more secure the encoding process is.
In a cryptographic system, an entity ensures whether other entities are approved through an authentication process. The authentication process is usually implemented in the form of a handshake protocol. During a handshake process, authenticating entities exchange the randomly generated data together with their identity identifications. After the result of the handshake process is analyzed, the decision of authenticating of a counterpart entity is made. In order to make the handshake process more secure and resistant to any man-in-the-middle attacks, a public key cryptographic system is often used.